Apparatus for manufacturing a golf ball with an initial preparatory form having a seam

ABSTRACT

A pair of unvulcanized half outer layer bodies are formed by metallic molds provided with first mold having a hemispherical convex portion and second mold having a hemispherical concave portion. A vulcanized inner core is put into either of half outer layer bodies, and a pair of half outer layer bodies are paired up to form a preparatory form which is to be vulcanization molded in metallic molds for vulcanization molding.

This application is a Division of prior application Ser. No. 08/890,990filed Jul. 10, 1997, now U.S. Pat. No. 6,036,907.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus and a method for manufacturing agolf ball, especially a golf ball having a multilayer structure.

2. Description of the Related Art

There are conventional methods for manufacturing a multilayer golf ball,and three of the methods are shown as follows, for example.

A first method for manufacturing a golf ball comprises the steps of,vulcanization molding an inner core, retaining the inner core at a fixedposition with a movable pin, injecting material which composes outerlayer by an injection molding machine or a transfer metallic mold,pulling off the movable pin, and vulcanization molding the outer layer.

A second method for manufacturing a golf ball comprises the steps offorming a pair of unvulcanized half outer layer bodies by metallicmolds, which consists of a hemispherical concave mold and ahemispherical convex mold (or forming a pair of half outer layer bodiesby heating the half outer layer bodies which is unvulcanized for a fixedtime so that not to shrink the half outer layer bodies), inserting aninner core vulcanization molded separately into the half outer layerbodies, and vulcanization molding the half outer layer bodies and theinner core.

A third method for manufacturing a golf ball is as set forth in thesecond method, wherein each of the outer layers are not shaped intohemispherical appearance but shaped in sheet appearance.

However the conventional methods described above are not suitable formanufacturing a golf ball having a multilayer structure.

When manufacturing a golf ball by the first method, a whole structure ofthe metallic mold apparatus is extremely complicated and a limitation ofpressure for injecting material causes decrease of a number of golfballs to be produced per one press and makes the method unsuitable formass production of golf balls. Furthermore it is difficult to fix adiametrical dimension of a hole portion of a metallic mold for insertinga movable pin. When a clearance between an outer circumferential face ofa movable pin and an inner face of a metallic mold hole portion is toosmall, the movable pin is not able to move smoothly, and if theclearance is too large, rubber is possible to outflow from thisclearance.

When manufacturing a golf ball by the second method, the metallic moldis opened after molding a half outer layer body and the adhesion of thehalf outer layer body either to convex mold or to a concave mold isunpredictable, and the method is impossible to mass-produce golf balls.The third method only differs from the second method for having thesheet appearance half outer layer body, and this method has the samedefects as the second method.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anapparatus and a method for manufacturing a golf ball wherein theseproblems are solved and are able to mass-produce

high quality golf balls having multilayer structures.

The present invention includes a pair of unvulcanized half outer layerbodies are formed by metallic molds provided with first mold having ahemispherical convex portion and second mold having a hemisphericalconcave portion. A vulcanized inner core is put into either of halfouter layer bodies, and a pair of half outer layer bodies are paired upto form a preparatory form which is to be vulcanization molded inmetallic molds for vulcanization molding.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to theaccompanying drawings, in which:

FIGS. 1A, 1B and 1C are respectively a schematic view of a golf ballaccording to the present invention;

FIGS. 2A and 2B are respectively a schematic view of a method ofmanufacturing a golf ball;

FIG. 3 is an enlarged sectional view of a principal portion of ametallic mold;

FIG. 4 is an perspective view of a device for folding;

FIG. 5 is an perspective view of the device for folding;

FIG. 6 is a schematic sectional view of a principal portion of paired upsecond molds;

FIGS. 7A, 7B, 7C and 7D are respectively a schematic view of a pairingup mechanism;

FIG. 8 is a schematic sectional view of a principal portion of secondmold of another apparatus for manufacturing a golf ball;

FIG. 9 is a schematic view of a preparatory form; and

FIGS. 10A, 10B and 10C are respectively a schematic view of acomparative method for manufacturing a golf ball.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings.

FIG. 1 and FIG. 2 show a method for manufacturing a golf ball accordingto the present invention. This method comprises the steps of wrapping avulcanized inner layer (inner core 23) with unvulcanized outer layers 24by metallic molds for preparatory forming (second mold 4 describedlater) and vulcanization molding the outer layers and the inner layer bythe metallic mold for vulcanization molding to manufacture a product (agolf ball of a multilayer structure). The metallic molds possess acavity shaped different from a cavity of a metallic mold forvulcanization molding (not shown) to form a preparatory form S₁.Specifically a metallic mold apparatus shown in for example, FIGS. 4 and5 is used for preparatory forming.

A metallic mold device comprises a metallic mold 5, as shown in FIGS. 1and 2, having a first mold 2 possessing a hemispherical convex portion 1and a second mold 4 having a hemispherical concave portion 3. The firstmold 2 and the second mold 4 form a cavity 10 which is hemisphericalshaped as shown in FIG. 1B. A radius of curvature 100 (See FIG. 3) of aconvex portion 1 of the first mold 2 is smaller than a radius of aninner core 23 described later.

The second mold 4 comprises a mold main body 6 and a slide object 7which fits into the mold main body 6. On the mold main body 6, a holeportion 8 is formed comprising a small diameter portion 8 a, a middlediameter portion 8 b and a large diameter portion 8 c where a concavespherical face is formed. The slide object 7 slidably fits to this holeportion 8. The slide object 7 possesses a shaft portion 7 a and a headportion 7 b which is formed at end of the shaft portion 7 a. The headportion 7 b is fit into the middle diameter portion 8 b of the mold mainbody 6. On upper surface of the head portion 7 b of the slide object 7,a depression 9 which provides a concave spherical surface is formed.

As shown in FIG. 3, a radius of curvature 101 of the large diameterportion 8 c of the mold main body 6 is fixed to be greater than a radiusof curvature 102 of the depression 9 of the head portion 7 b of theslide object 7. When the slide object 7 is fit into the mold main body6, the large diameter portion 8 c and the depression 9 are locatedcontinuously. Thus, two concave curved surfaces respectively have theirown radius of curvatures on a concave portion 3 of a second mold 4. Onan inner surface of the concave portion 3 of the second mold 4 (theinner surface of the large diameter portion 8 c of the mold main body 6,to be specific), a circumferential groove 11 is molded. Thecircumferential groove is for example, 0.5 mm to 2.0 mm in width W, and0.1 mm to 1.2 mm in depth T. As many of the circumferential grooves asis desired can be formed. On an upper opening portion of the concaveportion 3 of the second mold 4, a taper 18 which opens widely toward theoutside is formed.

The slide object 7 is pushed up as shown in FIG. 2B by a pushing upmechanism (not shown) and the head portion 7 b thereof is slipped outfrom the middle diameter portion 8 b of the hole portion 8 of the moldmain body 6. The pushing up mechanism is constructed, for example, by acylinder mechanism. The first mold 2 rises and falls by, for example, apressing device. When the mold 2 is in a descended position, the moldforms a cavity 10 together with the second mold 4.

The metallic mold apparatus mentioned above process a pair of bases 13,14 which are respectively provided with two pieces of first molds 4 ofthe metallic mold 5. The pair of bases 13, 14 are adapted to be movableby a device for folding 28 having a hinge mechanism H.

That is to say, on upper surface of the base 14, a plurality of blocks15 (In FIGS. 4 and 5, number of blocks 15 are three but blocks to beconstructed are not restricted to be three) are formed and on uppersurface of the base 13, a plurality of blocks 16 (In FIGS. 4 and 5,number of blocks 16 are two but blocks to be constructed are notrestricted to be two) are formed. The blocks 16 are placed between theblocks 15, and a shaft 12 is inserted into the blocks 15, 16. Afastening 17 (for example, a bolt) fastens the block 16 to the shaft 12.When the shaft 12 is rotated in the direction of arrow A, the base 14moves in the direction of arrow B and second molds 4 of the base 14 areput above second molds 4 of the base 13. Thus, the hinge mechanism Hincludes the shaft 12 and the blocks 15, 16.

A device for folding 28 is provided with a pinion 20 and a rack 21 whichis engaged with the pinion 20. The pinion 12 is continuously formed nextto the shaft 12, and the rack 21 is reciprocated by a reciprocatingmechanism (not shown). The pinion 20 rotates on the shaft 12, andcorresponding to this rotation, the base 14 moves in the direction ofarrows B and C.

A pair of molds 4 corresponding to each other are united as shown inFIG. 2A and concave portions 3 of the molds 4 are put together to form acavity 63, which puts half outer layer bodies 22 together to form apreparatory form S₁.

The number of second molds 4 to be respectively attached to each of base13, 14 is not limited to be two and the number thereof is free to beincreased or decreased as desired. A metallic mold apparatus having aplurality of pair of bases 13, 14 which second molds 4 are formed can beused.

Next, explained below is a method for manufacturing a golf ball usingthe metallic mold apparatus described above.

First, as shown in FIG. 4, the base 13 and the base 14 are horizontallysupported (i.e. the concave portions 3 of the second molds 4 of themetallic molds 5 are opened upwardly). As shown in FIG. 1A, aftercasting short cylindrical or discoid materials (raw rubber) S forforming the outer layer into each of the concave portions 3 of each ofthe second molds 4, the first mold 2 is lowered. As shown in FIG. 1B, acavity 10 is formed by this first mold 2 and the second mold 4, and anunvulcanized half outer layer body 22 is molded. The amount of time forpressing in this situation is for example, approximately 5 seconds.After that, the first mold 2 is raised. Once the first mold 2 is raised,depending on the form of the concave portion 3 of the second mold 4, themolded half outer layer body 22 adheres to the second mold 4.

A residual stress in material (raw rubber) S must be removed, and it isdesirable that the material is treated by heating without transformationand vulcanization of rubber. As a condition of the heat treatment, whena heating temperature is X° C., it is preferable that the material isheated for 2×2^(((140−X)/10)) minutes. Precisely, it is heated by atemperature of 40° C. to 140° C. for 2 minutes to 35 hours.

Next, as shown in FIG. 1C, a vulcanized inner core 23 is inserted intothe half outer layer body 22 of the second mold 4 (on base 13 side). Thesecond mold 4 and a corresponding second mold 4 of the other metallicmold 5 (a half outer layer body 22 is adhered to this second mold 4) isput together as shown in FIG. 2A, and an unvulcanized golf ball (apreparatory form S₁) is formed. To be specific, the rack 21 is drivenand the pinion 20 is rotated to move the base 14 and the correspondingsecond molds 4 are paired up to form a preparatory form S₁ in the cavity63. Pressure is applied to the second mold 4 by a press apparatus (notshown) which makes the first mold 2 ascend and descend. An amount oftime for pressurizing is for example, approximately 10 seconds. Theradius of curvature 100 of the convex portion 1 of the first mold 2 isarranged, as described above, smaller than a radius of the inner core23, and adhesiveness between the inner core 23 and the outer layer 24which is to be formed increases. The difference between the radius ofcurvature 100 of the convex portion 1 and the radius of the inner core23 is preferred to be 2 mm or less. If the difference exceeds 2 mm,excessive force which causes eccentricity between the outer layer 24 andthe inner core 23 is generated when the outer layers are pressedtogether.

In concrete terms, a diameter r₁ of the convex portion 1 of the firstmold 2 arranged to be 0.9 mm≦r₁≦19 mm, and a diameter r₂ of the innercore 23 arranged to be 1 mm≦r₂≦19 mm are restricted as shown in thefollowing Formula 1: $\begin{matrix}{0.10 \geq \frac{r_{2} - r_{1}}{r_{2}} \geq 0} & \text{Formula~~1}\end{matrix}$

When a diameter r₀ of a vulcanization molded outer layer 24 is fixed as18.4 mm ≦r₀≦19.8 mm, a diameter r₂ of the inner core 23 is arranged tobe r₀>r₂, a radius of a depression 9 is expressed as r₃, and an amountof offset of the radius r₃ is arranged to be 3≦d₃≦8, a radius of a largediameter portion 8 c is expressed as r₄, and an amount of offset of theradius r₄ is fixed to be 1≦d₄≦3 and, d₄+2≦d₃, so that r₃+d₃>r₄+d₄>r₀ isto be satisfied.

After a preparatory form S₁ is molded, the rack 21 is driven and thepinion 20 is rotated for moving the base 14 and for opening thecorresponding second molds 4. As shown in FIG. 2B, the slide object 7 israised, an unvulcanized golf ball (the preparatory form S₁) is taken outfrom the second mold 4, and the preparatory form S₁ is vulcanizationmolded by a metallic mold for vulcanization molding (not shown) formolding golf balls (products).

By using the metallic mold for manufacturing a golf ball as mentionedabove, putting materials into the second molds 4 is performed withoutdifficulty because the concave portions 3 of the second molds 4 areupwardly opened, and there is no need for removing from the second molds4 of the metallic mold 5 to a metallic mold for preparatory molding,because the second molds 4 of the metallic mold 5 for molding half outerlayer bodies can be also used as a metallic mold for preparatory moldinga pair of paired up half outer layer bodies 22, and thus, the operationefficiency for manufacturing a golf ball improves.

The circumferential groove 11 is provided on the inner surface of theconcave portion 3 of the second mold 4, and thereby, rubber flows intothe circumferential groove 11 when the half outer layer body 22 ismolded. As the metallic molds are opened, the half outer layer body 22sticks to the second mold 4 side for certain. As described above, thewidth W of the circumferential groove 11 is arranged to be 0.5 mm to 2.0mm and thickness T thereof is fixed to be 0.1 mm to 1.2 mm. If the widthW is less than 0.5 mm and the thickness T is less than 0.1 mm, a part ofrubber which catches the half outer layer body 22 turns out to be small.Conversely, if the width W is more than 2.0 mm and the thickness T ismore than 1.2 mm, the circumferential groove is so large that taking outa preparatory form S₁ from the mold becomes difficult.

When the preparatory form is taken out from the mold, the slide object 7of the second mold 4 is pushed up, and the preparatory form S₁ is notgiven excessive force and is brought out easily and reliably, withouttransformation.

Next, Table 1 shows examples of the present invention (in case an outerlayer 24 having radius of 19.83 mm is provided around an inner core 23having a radius of 12 mm).

As a first example (example 1) of the invention, the curvature of radius100 of the convex portion 1 is arranged to be 11.5 mm, the curvature ofthe radius 101 of the large diameter portion 8 c is fixed to be 19 mm,and the curvature of radius 102 of the depression 9 is arranged to be 17mm. The metallic mold 5 has an eccentricity d of a central point of aradius of curvature 102 of the depression 9 and the radius of curvature100 of the convex portion 1 is arranged to be 6 mm when the first mold 2and the second mold 4 are united. Manufacturing golf balls (products) byusing the metallic mold 5, inspecting conditions of products, andresults of inspections are shown in Table 1. In this case, on theconcave portion 3 of the second mold 4, the circumferential groove 11 isformed and the second molds 4 are also used as metallic molds forbonding half outer layer bodies together after setting an inner coretherein.

TABLE 1 conventional conventional conventional example example exampleexample example example 1 2 3 1 2 3 number of gulf 213 213 213 53 24 100balls produced per 1 hour/per 1 apparatus (regard a core method as 100)adhesion on 0/600 0/600 0/600 — — 498/600 convex portion side (number)eccentricity (mm) 0.25 0.30 0.28 0.39 0.40 0.41 (average) depression on0/600 0/600 0/600 3/600 16/600 37/600 surface (number) adhesion betweengood good good good good normal layers

As a second example (example 2) of the invention, the curvature ofradius 100 of the convex portion 1 is arranged to be 11.25 mm, thecurvature of radius 101 of the large diameter portion 8 c is fixed to be18.5 mm, and the curvature of radius 102 of the depression 9 is arrangedto be 16.5 mm. The metallic mold 5 has an eccentricity d of a centralpoint of the radius of curvature 102 of the depression 9 and the radiusof curvature 100 of the convex portion 1 arranged to be 8 mm when thefirst mold 2 and the second mold 4 are united. Manufacturing golf balls(products) by using the metallic mold, inspecting conditions ofproducts, and results of inspections are shown in Table 1. In this case,on the concave portion 3 of the second mold 4, the circumferentialgroove 11 is formed and the second molds 4 are used as metallic moldsfor sticking half outer layer bodies together after setting an innercore therein.

As a third example (example 3) of the invention, the curvature of radius100 of convex portion 1 is arranged to be 11.75 mm, the curvature ofradius 101 of the large diameter portion 8 c is fixed to be 18.5 mm, andthe curvature of radius 102 of the depression 9 is arranged to be 17.5mm. The metallic mold 5 has an eccentricity d of a central point of theradius of curvature 102 of the depression 9 and the radius of curvature100 of the convex portion 1 arranged to be 8 mm when the first mold 2and the second mold 4 are united. Manufacturing golf balls (products) byusing a metallic mold 5, inspecting conditions of products, and resultsof inspections are shown in Table 1. In this case, the second molds 4are also used as metallic molds for bonding half outer layer bodiestogether after setting an inner core therein, but the circumferentialgroove 11 is not formed on the concave portion 3 of the second mold 4.

In example 1 of the invention, the radius of the inner core 23 is fixedto be 0.5 mm smaller than the radius of curvature 100 of the convexportion 1. In example 2 of the invention, the radius of the inner core23 is fixed to be 0.75 mm smaller than the radius of curvature 100 ofthe convex portion 1. In example 3 of the invention, the radius of theinner core 23 is fixed to be 0.25 mm smaller than the radius ofcurvature. 100 of the convex portion 1.

In comparison, golf balls manufactured using the conventional method areinspected and results are shown as conventional examples 1, 2, 3.Conventional example 1 is the first method described as a prior art andan injection molding machine is used in this method. Conventionalexample 2 is the first method described as a prior art and a transfermetallic mold is used. Conventional example 3 is the second methoddescribed as a prior art. Golf balls of the conventional examples arerespectively manufactured by the conventional method.

In Table 1, the number of golf balls manufactured per hour, per anapparatus obtained in conventional example 3 is 100. It is apparent thatexamples of the present invention can produce numerous balls, thusproving the efficiency of the present inventions. Adhesion of a halfouter layer body to a first mold having a convex portion did not occurin examples of the present invention. However, in conventional example3, 498 balls out of 600 balls had the adhesion to the first mold.Efficiency in operation of the present invention is proved with thisresult. With regard to an amount of eccentricity, the result of examplesof the present invention is approximately 0.1 mm less than the resultsof conventional examples. Balls with a recess on the surface were notfound in examples of the present invention. However, 3 out of 600 ballsin conventional example 1, 16 out of 600 balls in conventional example2, and 37 out of 600 balls in conventional example 3 were recessed onthe surface.

The number of golf balls manufactured per hour, per an apparatus arecalculated as shown below.

 (Number of golf balls produced per an apparatus in a cycle)×(cycles peran hour)

An angle of inclination θ of the taper 18 is arranged to be not lessthan 25° but below 30° as shown in FIG. 6. The taper 18 is provided at alocation H which is specifically not less than 2.0 mm but 8.0 mm or lessfrom a joining face 65 of the mold 4. The angle of inclination θ is anangle of inclination to a center line of the metallic mold.

If there is a subtle transformation or inequality in thickness ofunvulcanized layers (half outer layer bodies 22) of a preparatory formS₁, when the molds are closed while press vulcanization molding the halfouter layer bodies 22, rubber is apt to flow to a thick part of theunvulcanized layers as compared to a thin part thereof. The thick partgets thicker and thin part becomes thinner, thus causing a greateccentricity of vulcanized inner core 23. When molding an unvulcanizedgolf ball (a preparatory form S₁), by using a mold not provided withtaper 18 on an inner circumferential rim of the opening of the concaveportion 3 and putting the half outer layer bodies 22 together, as shownin FIG. 10A, with the passage of time, the outer layer bodies shrink,and adhered parts are separated and a so called opening occurs andeccentricity of the vulcanized inner core 23 is caused.

If the outer layer bodies are vulcanization molded while the outer layerbodies are opened, as shown in FIG. 10B, rubber between the openingportion and the opposite side thereof flows so well that the inner core23 is pushed off to the opening side, and the inner core 23 of a productP becomes eccentric as shown in FIG. 10C.

According to the present invention, the molds 4 having the taper 18 oninner circumferential rim of the opening of the concave portion 3 areused. When putting half outer layer bodies together, a seam portion 25which swells out and forms an outer blade is formed on a joining faceportion (equator portion) of a preparatory form S₁. Therefore, thebonding area becomes large and even with the passage of time.Accordingly, part of the bonding area will not open (will not be acondition of opening). However even with this case, if there is anunequal portion of rubber volume of seam portion 25, rubber flows toenlarge the unequal portion when vulcanization pressing, and induceseccentricity of the inner core 23. That is to say, the less the rubbervolume of the seam portion 25, the less the chance of inducingeccentricity. However, a small volume of rubber in the seam portion 25causes an easy opening and a separating of the seam portions.

The volume of rubber in seam portion 25 needs to be optimized. Forinstance, the angle of inclination θ of the taper 18 can be arranged tooptimize the volume of rubber in the seam portion 25.

To be specific, when the angle of inclination θ of the taper 18 is lessthan 25° or when the taper 18 is formed at a location below 2.0 mm fromthe joining face, the joining area is insufficient and an opening andeccentricity of the bonded surfaces are induced. On the other hand, whenthe angle of inclination θ of the taper 18 is 30° or more or when thetaper 18 is formed at a location over 8.0 mm from a joining face, rubberin the seam portion 25 becomes excessive in volume and rubber flows toomuch and induces eccentricity.

To avoid separating the bonding faces of the half outer layer bodies 22without forming the seam portion which expands like an outer blade,using an adhesive agent or extending the amount of time of applyingpressure can be thought of. However using of the bonding agent becomes acause for producing products of varying quality, and increases anotherprocess of manufacturing, such as increased costs and extended amountsof time for pressurizing, which leads to decreased productivity.

A mold of a pair of molds 4 can be movable through the pairing upmechanism 57 as shown in FIGS. 7A to 7 D. The pairing up mechanism 57comprises for example, a propping mount 58 for receiving a base 61supporting the mold 4 movable through a shaft 60, and a cylinder 59which makes the propping mount 58 descend and ascend. Therefore, apiston rod 59 a of the cylinder 59 is elongated in the direction ofarrow F in FIG. 7B and makes the propping mount 58 and the mold 4 riseas illustrated in the FIGS. 7A to 7B. After that, as shown in FIG. 7C,the mold 4 is moved on an axis 10 in the direction of arrow F, and amold 4 can be positioned right above the other mold 4 so that theconcave portions 3 thereof respectively face each other. As shown inFIG. 7D, the piston rod 59 a of the cylinder 59 is lowered in thedirection of arrow G and the pair of molds 4 can be put together.Therefore, a pairing up mechanism 57 makes it possible to lower one mold4 vertically toward the other mold 4. When the molds 4 are put togetheras shown in FIG. 7D, a stopper (not shown) is provided to control thebase 61 so as not to move on the axis 60.

Thus, the mold 4 without the vulcanized inner core 23 is loweredvertically to pair up together with the other mold 4 having thevulcanized inner core 23 by the pairing up mechanism 57.

A direction for pressurizing can be arranged to be vertical and aninequality of pressure on uniting molds can be prevented, and apreparatory form S₁ which is to be formed is not opened on a joiningface and an vulcanized inner core 23 does not become eccentric.

FIG. 8 shows another embodiment of the present invention. In this case,on an inner circumferential rim of the opening of the concave portion 3,a first taper 67 and a second taper 68 are formed. The first taper 67 onan outer side and the second taper 68 on an inner side are formedsuccessively.

An angle of inclination θ₁ of the first taper 67 is arranged to belarger than an angle of inclination θ₂ of the second taper 68 and theangle of inclination θ₁ is arranged to be not less than 30° but lessthan or equal to 80°. The first taper 67 and the second taper 68 areformed at a location which ranges 0.5 mm or more and 8.0 mm or less froma joining face 65 of the mold 4.

Therefore, a seam portion 25 which possesses an optimum volume of rubberis formed on a preparatory form S₁ by using the mold 4. If an angle ofinclination θ₁ of the first taper 67 is arranged to be below 30° orformed at a location below 0.5 mm from the joining face, the bondingarea is too small to cause an opening of seam portion or to induce aneccentricity. If an angle of inclination θ₁ of the first taper 67 isarranged to be more than 80° or if the taper 67 is formed at a locationmore than 8.0 mm from the joining face, the rubber volume of the seamportion 25 becomes too large and rubber flows too much, thus inducing aneccentricity. If an angle of inclination θ₁ of the first taper 67 isarranged to be smaller than an angle of inclination θ₂ of the secondtaper 68, flow of rubber to an opening portion is too much and causes aneccentricity when the molds are closed when press vulcanizing.

Material S is preferable to be heated within the limits such thattransformation of the material is not caused and vulcanization of rubberis not caused, and the heating of the material is possible to reduceopening of bonded outer layers and eccentricity remarkably. The amountof time for this heat treatment differs depending on temperature forheating because the relaxation mechanism of the residual stress includesthermal activation of polymer molecule movement, and the amount of timefor treatment is arranged to be an Arrhenius type and it is set to be2×2^(((140−x)/10)) minutes as described above. That is to say, if thetemperature is arranged to be over 140°, a so called burn occurs and ifit is below 40°, the amount of time for treatment becomes too long andlowers productivity. Regarding the amount of time for heat treatment, itis not possible to transfer heat into the inner layer sufficiently ifthe time is below 2 minutes. And conversely, it causes lowering inproductivity if the time is over 35 hours.

To ensure that the half outer layer 22 adheres to the mold 4 side and toimprove efficiency of productivity of late manufacturing process, acircumferential groove is preferred to be formed on the inner surface ofthe concave portion 3 of the mold 4 as shown in FIG. 8.

Results of examples of the invention are shown below.

Various molds 4 are formed to manufacture golf balls, and a percentage(%) of opening occurred to the balls, and an amount of eccentricity (mm)of the balls were inspected as shown in examples 4 to 9 of the presentinvention, as set forth in Table 2. In the examples, 60 balls arechecked in each experiment respectively.

TABLE 2 example example example example example example 4 5 6 7 8 9Condition Taper 1 stage 2 stages 1 stage 1 stage 1 stage 1 stage 28.4°first taper 66.4° 11.3° 11.3° 11.3° 11.3° second taper 28.4° Pairing upNo No Yes No No No Mechanism Heating No No No 80° C. × 40° C. × 130° C.× Treatment 1 hr 34 hrs 5 mins Percentage (%) of opening 1 2 2 4 5 6 ofbonded outer layers (n = 60) Eccentricity (mm) 0.22 0.35 0.31 0.32 0.330.35 (n = 60)

In Table 2, in the column of Taper, “1 stage” means that one taper 18was formed and “2 stages” means that, as shown in FIG. 8, first andsecond tapers 67, 68 were formed. In each of examples 4 to 9 of theinvention, there was little occurrence of opening, and the amount ofeccentricity was slight.

For purposes of comparison, as shown in comparative examples 1 to 6 inTable 3, various molds are formed for manufacturing golf balls, and apercentage (%) of the balls whose joining face opened, and the amount ofeccentricity (mm) of the balls were inspected. 60 balls were checked ineach experiment respectively. In Table 3, in column of Taper, “1 stage”means that one taper 18 was formed and “2 stages” mean that, as shown inFIG. 8, first and second tapers 67, 68 were formed.

TABLE 3 comparative comparative comparative comparative comparativecomparative example example example example example example 1 2 3 4 5 6Condition Taper 1 stage 1 stage 2 stages 2 stages 1 stage 1 stage 11.3°43.2° first taper 83° first taper 28.4° 11.3° 11.3° second taper 28.4°second taper 43.2° Pairing up No No No No No No Mechanism Heating No NoNo No 80° C. × 35° C. × Treatment 1 min 40 hrs Percentage (%) of opening34 4 3 45 68 42 of bonded outer layers (n = 60) Eccentricity (mm) 0.510.65 0.62 0.55 0.57 0.61 (n = 60)

As shown in Table 3, in comparative example 1, the angle of inclinationof the taper was below 25° and the percentage of the balls whose bondedfaces were opened was as great as 34%, and the amount of eccentricitywas also as large as 0.51 mm. In comparative example 2, the angle ofinclination of the taper was 30° or more and the percentage of openingamong the balls was small, however the amount of eccentricity was asgreat as 0.65 mm. In comparative example 3, the angle of inclination ofthe first taper was over 80° and the percentage of opening bonded outerlayers of the balls was small, however the amount of eccentricity was asgreat as 0.62 mm. In comparative example 4, the angle of inclination ofthe first taper was below 30° and angle of inclination of the secondtaper was greater than the angle of inclination of the first taper, thepercentage of opening of the bonded outer layers of the balls was asgreat as 45%, and the amount of eccentricity was also as great as 0.55mm. In comparative example 5, the angle of inclination of the firsttaper was below 25° and the material was heated at 80° C. for as short atime as 1 minute and the percentage of opening of the balls was as greatas 68%, and the amount of eccentricity was also as great as 0.57 mm. Incomparative example 6, the angle of inclination of the first taper wasbelow 25° and material was heated at 35° C. for 40 hours, and thepercentage of opening of the balls was as great as 42%, and the amountof eccentricity was also as great as 0.61 mm.

According to the present invention, a multilayer golf ball having aninner core (inner layer) of which eccentricity is small can bemanufactured by a simple method with reliability and at a low cost, andgolf balls can be mass-produced. By using a first mold processing ahemispherical convex portion and a second mold processing ahemispherical concave portion, golf balls without depression on surfacesor without faulty bonding layers can be produced without difficulty andwith reliability.

Using a mold which is provided with at least 2 kinds of concave curvedsurfaces respectively having a different radius of curvature, a pulsingstream of rubber is used to prevent a residual air layer which causesdepressions on surfaces of the products. Thus it is possible tomanufacture products without depressions. Using a metallic moldprocessing a convex portion with a radius of curvature thereof beingless than or equal to the radius of the vulcanized inner core, it ispossible to reliably bring outer layers into intimate contact with aninner core.

When the mold having a circumferential groove on an inner surface of aconcave portion is used, after forming a half outer layer body, and asthe mold is opened, the half outer layer body is adhered to the secondmold side for every time, which facilitates subsequent processes.

Second molds, which are to be united while having concave portions onwhich half outer layer bodies are adhered, can be used as a metallicmold for bonding half outer layer bodies after setting an inner coretherein, and the efficiency of manufacturing products improves, and itis possible to simplify a whole construction of the mold because it doesnot require another mold for bonding half outer layer bodies together.

Using an apparatus having a device for folding, when material is putinto a metallic mold, a concave portion of second mold can be upwardlyopened and materials are reliably placed into molds without difficulty.

An apparatus possessing a taper or two on an inner circumferential rimof an opening of a concave portion of the mold prevents an adheredsurface from being separated, while reliably preventing eccentricity ofinner core. Thus, it is possible for the apparatus to manufacture golfballs of high quality.

An apparatus having a mechanism putting a pair of molds together cancover a vulcanized layer with an unvulcanized layer with an uniformpressure, thus preventing the opening of the bonded outer layers andremarkably reducing eccentricity. If material made of raw rubber isheated in advance, eccentricity of an inner core can be preventedwithout fail, opening of the bonded outer layers can be reduced, andgolf balls are manufactured without using a large apparatus. If thetemperature of heating is X and if material S which is made of rawrubber is heated for 2×2^(((140−x)/10)) minutes, a burn will not becaused, and the time for manufacturing win not be too long andproductivity of the manufacturing apparatus is improved.

While preferred embodiments of the present invention have been describedin this specification, it is to be understood that the invention isillustrative and not restrictive, because various changes are possiblewithin the spirit of the indispensable features.

What is claimed is:
 1. An apparatus for manufacturing a golf ball,comprising: a pair of molds, each mold having a hemispherical concaveportion which acts as a cavity for uniting half outer layer bodies towrap a vulcanized inner core therein when each of said molds are puttogether after the half outer layer bodies are fixed to the molds, saidhemispherically concave portion being shaped differently from a cavityof separate molds for vulcanization molding of the united half outerlayer bodies having said vulcanized inner core therein, and each of saidhemispherical concave portions having an inner circumferential rim witha taper to form part of a seam on the united half outer layer bodieshaving said vulcanized inner core therein, wherein said taper isarranged to optimize the volume of the material of the half outer layerbody in said part of said seam.
 2. An apparatus for manufacturing a golfball, comprising: a pair of metallic molds, each mold having ahemispherical concave portion which acts as a cavity for unitingunvulcanized half outer layer bodies to wrap a vulcanized inner coretherein when said molds are folded together, said hemispherical concaveportion being shaped differently from a cavity of separate molds forvulcanization molding of the united unvulcanized half outer layer bodieshaving said vulcanized inner core therein, each of said hemisphericalconcave portions having an inner circumferential rim with a taper toform part of a seam on the united unvulcanized outer layer bodies havingsaid vulcanized inner core therein, wherein said taper is arranged tooptimize the volume of the material of the half unvulcanized outer layerbody in said part of said seam; and a device for folding said pair ofmetallic molds together, which positions one mold of said pair of moldsholding one of the unvulcanized half outer layer bodies over the othermold holding both the other one of the unvulcanized half outer layerbodies and the vulcanized inner core.
 3. An apparatus for manufacturinga golf ball, comprising: a pair of metallic molds, each mold having ahemispherical concave portion which acts as a cavity for unitingunvulcanized half outer layer bodies to wrap a vulcanized inner coretherein when said molds are paired together, said hemispherical concaveportion being shaped differently from a cavity of separate molds forvulcanization molding of the united unvulcanized half outer layer bodieshaving said vulcanized inner core therein, each of said hemisphericalconcave portions having an inner circumferential rim with a taper toform part of a seam on the united unvulcanized outer layer bodies havingsaid vulcanized inner core therein, wherein said taper is arranged tooptimize the volume of the material of the half unvulcanized outer layerbody in said part of said seam; and a pairing mechanism which verticallylowers one mold of the pair of molds holding one of the half outer layerbodies toward the other of said pair of molds holding both the other ofthe half outer layer bodies and the vulcanized inner core.
 4. Theapparatus for manufacturing a golf ball as set forth in claim 1, 2 or 3,wherein said taper gradually opens toward the inner circumferential rimof the concave portion at a location which is not less than 2.0 mm, but8.0 mm or less from a joining face, with an inclined angle θ of saidtaper being 25° or more but below 30° from the perpendicular.
 5. Theapparatus for manufacturing a golf ball as set forth in claim 1, 2 or 3,wherein said taper includes successively positioned first and secondtapers respectively opening toward the inner circumferential rim of theconcave portion at a location which is not less than 0.5 mm, but 8.0 mmor less from a joining face, with an inclined angle for the first taperbeing greater than an inclined angle of the second taper which isprovided inside of the first taper, and the inclined angle of said firsttaper being 30° and more, but 80° or less from the perpendicular.
 6. Theapparatus for manufacturing a golf ball as set forth in claim 1, 2 or 3,wherein said hemispherical concave portion has at least 2 differentkinds of concave curved portions respectively having different radius ofcurvature.
 7. The apparatus for manufacturing a golf bass as set forthin claim 1, 2 or 3, wherein each of the molds is provided with acircumferential groove on an inner surface of the hemispherical concaveportion.